The present invention relates to a printing exposure amount determining method and apparatus for a photographic printer which uses a zoom lens to make a trimming print, and more particularly to a method and apparatus for calculating an appropriate printing exposure amount in consideration of a reciprocity law failure raised dependent on the printing magnification.
In a general type of conventional photographic printer, photoprints are made at one of several magnifications in a discrete or stepwise manner, the magnification being determined by a frame size of a photographic film such as a negative film and a print size. A printing exposure condition is set in response to the stepwise magnification in the photographic printer. It also is known that a photographic printer can make a trimming print at any specified printing magnification by using a zoom lens.
However, in the photographic printer for trimming prints, the f-number of the zoom lens is varied corresponding to the magnification which is determined by a focal length of the zoom lens. Further, the exposure time changes corresponding to the magnification to such an extent that a reciprocity law failure of photographic paper increases considerably and is not negligible. Therefore, there is a problem in that an unchanged density of an image cannot be reproduced on the finished photoprint when the magnification is changed.
Therefore, it is an object of the present invention to provide a method and apparatus for determining the printing exposure amount, wherein a trimming print can be made at an appropriate density for an exposure at any specified magnification of the zoom lens.